In recent years, with respect to electronic equipments such as mobile equipments and information equipments, there is a rapid demand for reduction in size and higher performance. With this tendency, it has also been required to reduce a size of parts used in these equipments such as inductance devices and impart a high performance thereto. In particular, inductance devices used in power source circuits have been required to minimize the deterioration in inductance and the increase in core loss as DC bias characteristics observed when flowing AC current and DC current therethrough in a superimposed manner.
Conventionally, the DC bias characteristics of inductance devices have been improved by providing a structural magnetic gap inside thereof using Mn—Zn ferrite or Ni—Zn ferrite as a material thereof. Also, the core loss of the inductance devices has been reduced by controlling the composition of ferrite or adding additives thereto.
In particular, in the case of a multilayer inductance device which is produced by laminating a ferrite material and a non-magnetic material as a magnetic gap and baking these materials at the same time, there tends to arise such a problem that the resulting inductance device hardly exhibits desired properties owing to poor adhesion between these materials and differences in shrinkage ratio and thermal expansion coefficient therebetween, etc.
To solve the above problem, development of a ferrite material in which excellent DC bias characteristics are imparted to the magnetic material itself without provision of the structural magnetic gap, has proceeded. There are known Ni—Zn or Ni—Zn—Cu ferrite to which silicon oxide and zirconium oxide are added (Patent Document 1 and Patent Document 2), Ni—Zn—Cu ferrite to which silicon is added (Patent Document 3) and the like.
On the other hand, there have been proposed techniques for controlling a change in inductance of Ni—Zn—Cu ferrite owing to change in stress therein by incorporating Zn2SiO4 into the ferrite (Patent Document 4 and Patent Document 5).
Patent Document 1: Japanese Patent Application Laid-Open (KOKAI) No. 2003-112968
Patent Document 2: Japanese Patent Application Laid-Open (KOKAI) No. 2004-172396
Patent Document 3: Japanese Patent Application Laid-Open (KOKAI) No. 2005-145781
Patent Document 4: Japanese Patent Application Laid-Open (KOKAI) No. 2-137301
Patent Document 2: Japanese Patent Application Laid-Open (KOKAI) No. 2004-296865